This invention relates to computed tomographic (CT) imaging, and more particularly to methods and apparatus for motion correction.
Recent advancements in CT technology (faster scanning speed, larger coverage with multiple detector rows) have lead to new engineering challenges. For example, the latest technology multislice scanners employ increased scan speeds (0.5 second per revolution or less) and isotropic resolution (0.5 mm or less in X, Y, and Z) to support high resolution 3D clinical applications. Reducing artifacts in reconstructed images is one such engineering challenge. Specifically, reducing motion artifacts is desirable. For example, a method for correction of focal spot motion caused by thermal drift is described by Toth et al. in U.S. Pat. No. 6,185,275. However, this is a method that only corrects the projection data for the mean X axis position over a gantry rotation cycle. View to view position errors as a function of rotation angle or errors due to other factors are not corrected. Other methods to measure and adjust the X-axis position of the focal spot are described by Gard in U.S. Pat. No. 5,706,326 and Gard et al. in U.S. Pat. No. 5,550,889. Methods to measure and adjust the Z-axis position of the X-ray beam on the detector are also described by Toth et al. in U.S. Pat. No. 6,370,218 and Toth et al. in U.S. Pat. No. 6,385,279. However, the errors addressed by all the above methods are relative to the gantry system and not relative to the scan space. Hence, errors due to movement of the gantry system relative to the object being scanned are not corrected.